Device and method for carrying out heterogeneously-catalysed reactive distillations in particular for the production of pseudoionone

ABSTRACT

A column is described for carrying out reactive distillations in the presence of a heterogeneous particulate catalyst having an ordered packing or random packings which form intermediate spaces in the column interior, the quotient of the hydraulic diameter for the gas flow through the ordered packing or the random packings and the equivalent diameter of the catalyst particles being in the range from 2 to 20, preferably in the range from 5 to 10, in such a manner that the catalyst particles are introduced into the intermediate spaces, distributed and discharged loose under the action of gravity.

The invention relates to a column for carrying out reactivedistillations in the presence of a heterogeneous particulate catalyst,to a process for reactive distillation, and to a use.

In the prior art, various potential ways are known for carrying outheterogeneously catalyzed reactive distillations, that is to sayheterogeneously catalyzed reactions and at the same time separations bydistillation in the same column: one possibility is to coat packings ofa type known from distillation technology with the active catalystcomposition, for example as is the case with KATAPAK-M packing fromSulzer AG, CH8404 Winterthur. A disadvantage in this case is the factthat separate catalyst development is required to prepare activecatalyst compositions which can be applied to distillation packings,that the adhesion of the active catalyst compositions to the packings isfrequently limited and that relatively limited amounts of activecatalyst composition can be applied.

Therefore, columns for reactive distillation are more advantageous whichhave packings together with particulate catalysts. For this purpose itis known to introduce catalyst particles into pockets of wire mesh whicheither serve directly as distillation internals, such as the typeKATAPAK-S from Sulzer AG, CH8404 Winterthur, or which are designed asflat pockets which are laid between the individual layers of thedistillation packings, such as the type Multipak from Montz GmbH,D-40723 Hilden. These designs are also, however, limited with respect tothe amount of catalyst which can be accommodated and, in addition, aresusceptible to faults in operation, since predetermined liquid flowratesper unit area must be maintained precisely, which is difficult inpractice.

The Bales from CDTech, Houston, USA; are of a similar design, but thepocket structures are substantially coarser and therefore the separationefficiencies obtainable are lower. They are described, for example, inEP-A-0 466 954.

All designs having catalyst particles introduced in pockets have incommon the fact that filling and removing the catalyst particles islabor-intensive and time consuming.

In contrast, less complex designs are those in which the catalyst ispacked onto column trays and is there suspended in the liquid or isaccommodated in down columns from the column trays. These embodiments,however, are only suitable for very abrasion-resistant catalysts, whichis seldom the case in practice.

It is an object of the present invention to make it possible to useconventional particulate catalysts in reactive distillation columns andso to ensure simple charging of fresh catalyst and discharging of spentcatalyst, to reduce mechanical loading of the particulate catalyst byavoiding spouted beds and an excess inherent weight in the case of largebed heights and, furthermore, to homogenize the gas and liquid flowsover the column cross section.

We have found that this object is achieved by a column for carrying outreactive distillations in the presence of a heterogeneous particulatecatalyst having an ordered packing or random packings which forminterstices in the column interior.

In the invention the quotient of the hydraulic diameter for the gas flowthrough the ordered packing or the random packings and the equivalentdiameter of the catalyst particles is in the range from 2 to 20,preferably in the range from 5 to 10, in such a manner that the catalystparticles are introduced into the interstices, distributed anddischarged loose under the action of gravity.

It has thus been found that it is possible to charge a column equippedwith ordered packings or random packings directly with catalystparticles, without construction of additional reception spaces, forexample pockets, being necessary for this.

The hydraulic diameter is defined as is known as the ratio between fourtimes the area through which flow passes and the circumference thereof.Actual calculation of the same for a packing having linear folds isdescribed in the description of the figures in connection with FIG. 2.

The hydraulic diameter of random packings is determined via the porosityof the bed ψ, that is to say empty volume of the bed/total volume andthe equivalent diameter of the packings,${d_{hydraulic} = \frac{d_{p} \times \psi}{1 - \psi}},$where d_(hydraulic)=hydraulic diameter, d_(p)=diameter of the packingsand ψ=porosity. The equivalent diameter of the packings is defined bythe ratio between six times the volume and the surface area of therandom packing (see VDI Wärmeatlas [VDI thermal handbook], 5th edition,1988, Lk 1).

The equivalent diameter of catalyst particles present is defined by theratio between six times the volume and the surface area of the particle(see VDI Wärmeatlas [VDI thermal handbook], 5th edition, 1988, Lk 1).

Maintaining a quotient of the hydraulic diameter for the gas flowthrough the ordered packing or the random packings and the equivalentdiameter of the catalyst particles within the above defined rangeensures according to the invention that the catalyst particles areintroduced into the interstices of the ordered packing or the randompackings, distributed and discharged loose under the action of gravity.

With respect to the ordered packings or random packings which can beused, there are in principle no restrictions: column internals can beused which are regularly used in distillation technology in order toincrease the interfacial area between the phases migrating through thecolumn in countercurrent, the gaseous phase and the liquid phase. Theordered packings or random packings in the column interior forminterstices which in principle must be connected to one another toensure the counterflow of gaseous and liquid phases which is requiredfor the separation action by distillation.

The inventors have thus found that it is possible in principle tointroduce catalyst particles into the mutually connected intersticeswhich make up the ordered packing or random packings in the columninterior, to distribute them and discharge again the spent catalystparticles loose under the action of gravity.

It must be ensured here that sufficient free interstices are present forthe gas flow resulting in distillation, so that there is no backing upof the liquid stream flowing in countercurrent to the gas stream. Thisis ensured according to the invention by the quotient of the hydraulicdiameter for the gas stream through the ordered packing or through therandom packings and the equivalent diameter of the catalyst particlesbeing selected very small, that is to say having values in the abovedefined ranges.

The invention is not limited with respect to the shape and size of theusable catalyst particles; however, to improve the space-time yield ofheterogeneously catalyzed reactions, high specific surface areas andthus small catalyst particles are preferred. In beds of catalystparticles, as is known, the pressure drop increases with increasinglysmaller catalyst particles and limits, in the case of a reactivedistillation, the liquid and vapor throughputs to uneconomically smallvalues. Because of the generally highly pronounced channeling of liquidin catalyst beds, for large column diameters which are required inindustrial-scale plants, only low separation efficiencies bydistillation are achieved. These disadvantages have prevented hithertothe use, which is desirable per se, of catalyst beds as separationinternals in reactive distillations. In contrast, according to theinvention, precisely small catalyst particles which are also preferredwith respect to catalytic activity, are particularly suitable forcombined use with an ordered packing or with random packings, since theyare simpler to introduce the smaller are their dimensions compared withthe dimensions of the interstices of the ordered packing or randompackings.

The catalyst particles are preferably unsupported catalysts, but it isalso possible to use supported catalysts. With respect to the shape ofthe catalyst particles there are in principle no limitations, frequentlysolid or hollow cylinders, spheres, saddles or honeycomb or star-shapedrods are used. Suitable dimensions of the catalyst particles are, forexample for solid cylinder catalyst particles from about 1.5×4 to about4×8 mm.

According to the invention the interstices which the ordered packing orthe random packings make up in the column interior are such that thecatalyst particles are introduced into the interstices, distributed anddischarged loose under the action of gravity.

Preferably, as column internals, structured packings are used, that isto say ordered packings made up systematically in a regular geometryhaving defined passage regions for counterflow phases. Ordered packingsare generally made up of metal sheets, expanded metal layers or wiremesh layers essentially arranged in parallel to one another. Orderedpackings, compared with other column internals, are distinguished by ahigher load capacity, improved separation efficiency and a lowerspecific pressure drop. Packings are generally made up of corrugatedmetal sheets, expanded metal layers or mesh layers, essentially arrangedin parallel to one another, having usually linear corrugations whichsubdivide the sheet metal packing, the expanded metal layer or meshlayer into corrugated surfaces and in which case the angle ofinclination of the corrugated surface to the vertical is usually from 30to 45°. For the present invention, ordered packings having an angle ofinclination of the corrugated surface to the vertical in the range from10 to 45°, preferably 30°, can be used. By arranging successive orderedpacking sheets at the same angle of inclination to the vertical, butwith reversed sign, the known cross-channel structures are produced, asare exhibited, for example, by packings of the types Mellapak, CY or BXfrom Sulzer AG, CH-8404 Winterthur or types A3, BSH, B1 or M from MontzGmbH, D-40723 Hilden.

For use in reactive distillation, preferably, special embodiments ofstructured packings are used which permit an increased gas flow.

In a particularly preferred embodiment, one or more ordered sheet metalpackings of high specific surface area are arranged in alternation withone or more ordered sheet metal packings of low specific surface area.As a result intermediate spaces each having different hydraulic diameterare formed. Particularly preferably, the specific surface areas of theordered sheet metal packings are chosen in such a manner that firstlyintermediate spaces are formed for which the quotient of hydraulicdiameter and equivalent diameter of the catalyst particles is <1, andsecondly intermediate spaces for which the quotient of hydraulicdiameter and equivalent diameter of the catalyst particles is >2, inparticular in the above defined range from 2 to 20, in particular from 5to 10. No catalyst particles are charged into the first-mentionedintermediate spaces having a ratio of hydraulic diameter and equivalentdiameter of catalyst particles <1, the same are according to theinvention only charged into the intermediate spaces in which saidquotient is >2. This particular embodiment ensures an increased gas flowwith low pressure drops.

Preferably, the starting material for inventive ordered packings isusually additionally supplied with openings, for example with circularholes of diameter from about 4 to 6 mm, in order to increase theflooding point of the ordered packing and to enable higher columnloading. Flooding point of an ordered packing is the volume of gas orliquid per time and per unit area of cross section in which thetrickling liquid is backed up or entrained by the gas stream in andabove the packing to the point of complete flooding. Exceeding thisloading causes a rapid decrease in separation efficiency and a sharpincrease in pressure drop.

Instead of ordered packings, equally, random packings can be used, inwhich case, in principle, there are no limits with respect to the shapeof the same. Thus, for example, all shapes of random packings known indistillation technology can be used, such as Raschig rings, Pall ringsor saddles.

Ordered packings or random packings which have horizontal surfaceportions are advantageous. The horizontal surface portions receive someof the weight of the catalyst particles and divert it to the columnwall. As a result the mechanical loading of the catalyst is decreased.

Preference is given to ordered packings which are formed from orderedsheet metal packings for vertical installation into the column havinglinear corrugations which subdivide the ordered sheet metal packing intocorrugated surfaces, the angle of inclination of the corrugated surfacesto the horizontal being in the range from 90 to 45°, preferably 60°.

The specific surface area of packings for distillation is from about 250to 750 m²/m³. For columns for carrying out heterogeneously catalyzedreactive distillations, ordered packings having lower specific surfaceareas, in the range from about 50 to 250 m²/m³ are preferably used.

In the case of ordered packings for distillation, wall thicknesses ofthe metal sheets of typically from 0.07 to 0.1 mm suffice. In contrast,in the case of heterogeneously catalyzed reactive distillations,depending on catalyst weight and mechanical stability of the catalystgrains, wall thicknesses of the metal sheets in the range from 0.1 to 5mm, preferably from 0.15 to 0.3 mm, are used.

Preferably, ordered packings or random packings are used which have areduced resistance to flow at their surface, this reduced resistance toflow being achieved in particular by perforations and/or roughness ofthe material of the ordered packing or of the random packings or byconstructing the ordered packing as expanded metal. The perforationshere are preferably dimensioned with respect to their number anddimensions in such a manner that at least a proportion of 20%,preferably a proportion of from 40 to 80%, of the liquid reactionmixture passes through these perforations and flows onto the catalystparticles lying beneath them.

In a preferred embodiment, the ordered packing material consists ofexpanded metal, the ordered packing material being constructed in such amanner that the liquid flowing off on the packing material as film canflow off as completely as possible through the packing materialdownward, dripping being reinforced by outlet edges.

Preferably, the perforations are provided in the vicinity of the lowercorrugated edges of the ordered sheet metal packings arranged verticallyin the column, as described in DE-A 100 31 119. As a result, the fluidis preferably passed onto the upper side of the inclined corrugatedsurfaces and the liquid loading on the critical lower side is decreased.For this, ordered packings made of ordered sheet metal packings are usedfor vertical installation into the column having linear corrugationswhich subdivide the ordered sheet metal packings into corrugatedsurfaces and which have a width a, measured from corrugated edge tocorrugated edge, and perforations, and in which a proportion X of atleast 60% of the perforations has a distance b of at most 0.4 a to thelower corrugated edge of each corrugated surface. Preferably, theproportion of the area taken up by the perforations of a corrugatedsurface is from 5 to 40%, in particular from 10 to 20%, of thiscorrugated surface.

In a further preferred embodiment, the ordered packing is formed fromrippled or corrugated layers, and between two rippled or corrugatedlayers in each case one flat intermediate layer is disposed, in whichcase the flat intermediate layers do not extend to the edge of theordered packing or have, in the edge zone of the ordered packing, anincreased gas permeability, in particular holes, in accordance with DE-A196 01 558.

It is also possible to provide, instead of flat intermediate layers,less intensively rippled or corrugated layers.

The term edge zone of the ordered packing is applied to a concentricvolume element which extends from an outer cylinder surface to an innercylinder surface (the ordered packings typically have a cylindricalshape), with the outer cylinder surface being defined by the outer endsof the rippled or corrugated layers and the inner cylinder surface beingdefined by the outer ends of the flat layers. The horizontal lineconnecting the inner cylinder surface to the outer cylinder surface andwhich is oriented in parallel to the packing layers and passes throughthe column axis intersects from one to twenty, preferably from three toten, channels formed by each of the layers disposed next to one another.In the case of flat layers which do not extend into the edge zone, thusup to twenty channels are cleared next to one another in the edge zone.Second layers extending into the edge zone are preferably gas permeableon from 20 to 90% of their surface, particularly preferably from 40 to60% of their surface, that is to say, for example, provided with holes.

At the points at which the channels formed by the metal sheets contactthe column wall, damming of the ascending gas stream occurs, because thechannels are closed by the column wall. This leads to a markedly poorerseparation efficiency of the ordered packing. By opening the orderedpacking channels in the wall zone, this cause of a decreased separationefficiency can be eliminated in a simple and effective manner. The gascan in this case transfer from the channels ending at the column wallinto other channels which lead it in the opposite direction.

The invention also relates to a process for reactive distillation in acolumn which is fitted, as described above, with an ordered packing orrandom packings together with a bed of catalyst particles. Preferably,the column is operated with respect to its gas and liquid loadings insuch a manner that a maximum of from 50 to 95%, preferably from 70 to80%, of the flooding limit loading is reached.

The invention also relates to the use of the above described column andthe process for carrying out heterogeneously catalyzed reactivedistillations, in particular acid- or base-catalyzed equilibriumreactions, particularly preferably for preparing pseudoionone byaldolizing citral and acetone in the presence of analuminum-oxide-supported praseodymium catalyst.

The invention will now be described in more detail below with referenceto a drawing and an example.

In the drawings

FIG. 1 shows a diagrammatic representation of an embodiment of aninventive ordered packing,

FIG. 2 shows a diagrammatic representation of an ordered sheet metalpacking having linear corrugations and

FIG. 3 shows a diagrammatic representation of an ordered sheet metalpacking having perforations and

FIG. 4 shows a diagrammatic representation of an embodiment of aninventive column.

The diagrammatic representation in FIG. 1 shows an ordered packing 1having ordered sheet metal packings 2 which have linear corrugations 5with formation of corrugated surfaces 6, with in each case anintermediate space 3 being formed between two sequential ordered sheetmetal packings 2. According to the invention catalyst particles 4 arecharged into the same intermediate space.

FIG. 2 shows diagrammatically an ordered sheet metal packing 2 havinglinear corrugations 5 and corrugated surfaces 6. a is the width of acorrugated surface 6 measured from corrugated edge 5 to corrugated edge5, c represents the distance between two adjacent corrugated edges 5 andh represents the height of a corrugation.

FIG. 3 shows diagrammatically a particular embodiment of an orderedsheet metal packing 2 having corrugated edges 5, corrugated surfaces 6and a width a of the corrugated surfaces 6 having perforations whichhave a distance b from the lower corrugated edge 5 of each corrugatedsurface 6.

The reactive distillation column 7 shown diagrammatically in FIG. 4 hastwo pure separation zones 8, respectively in the upper and lower regionof the reactive distillation column 7, which are fitted with structuredfabric packings. In the middle column region is arranged a reaction zone9 which has a lower region 9 a containing an ordered packing withoutintroduced catalyst particles and an upper region 9 b containing aninventive packing having introduced catalyst particles. The reactivedistillation column 7 is fitted with a bottoms reboiler 10 and acondenser 11 at the column top. The starting materials are applied inthe upper region of the column as streams I and II, the reaction mixtureis taken off as bottom stream III and a top stream IV is taken off atthe column top. A pressure controller PC is disposed at the column top.

EXAMPLES Example 1 Loose Packing Experiments

A column section having a diameter of 0.3 m was fitted with two ordereddistillation packings arranged offset by 90° of type B1 from Montz, theheight of each ordered packing being 23 cm. Catalyst particles wereintroduced by loose packing into the ordered distillation packings. Thefed volume and the ease of handling during introduction and removal ofthe catalyst particles were determined. The catalyst particles used weresolid cylinders of γ-Al₂O₃ and TiO₂. The solid γ-Al₂O₃ cylinders of adiameter of 1.5 mm and a height of from 1 to 4 mm have an equivalentparticle diameter of 2 mm. The solid TiO₂ cylinders of a diameter of 4mm and a height of from 2 to 10 mm have an equivalent particle diameterof 5 mm.

-   1A) Loose packing experiments using solid γ-Al₂O₃ cylinders,    diameter 1.5 mm. Ordered packings of type B1 from Montz each having    different specific surface areas and different angles of inclination    of the corrugated surfaces to the horizontal were used.-   1A₁) A sheet metal packing of type B1-125.80 having a specific    surface area of 125 m²/m³ and an angle to the horizontal of 80° was    used. 90% of the superficial volume was packed with the    abovementioned catalyst particles. The ordered packing had a    hydraulic diameter of 19 mm. The catalyst was able to be introduced    very readily and in the dry state also trickled out again    completely. The ratio of the equivalent diameter of the catalyst    particles to the hydraulic diameter of the ordered packing was 9.-   1A₂) An ordered packing of type B1-250.80 having a specific surface    area of 250 m²/m³ and an angle to the horizontal of 80° was packed    with the abovementioned catalyst particles. In this case 80% of the    superficial volume was able to be packed with catalyst particles.    The ordered packing had a hydraulic diameter of 9.4 mm. The catalyst    was able to be introduced very readily and in the dry state also    trickled out again completely. The ratio of equivalent diameter of    the catalyst particles to the hydraulic diameter of the ordered    packing was 4.7.-   1A₃) A packing of type B1-250.60 was used, that is to say having a    specific surface area of 250 m²/m³ and an angle of 60° to the    horizontal. 80% of the superficial volume of the same was able to be    packed with the abovementioned catalyst particles. The ordered    packing had a hydraulic diameter of 9.4 mm. The catalyst was able to    be introduced very readily and in the dry state also trickled out    again completely. The ratio of the equivalent diameter of the    catalyst particles to the hydraulic diameter of the ordered packing    was 4.7.-   1B) Solid TiO₂ cylinders, diameter 4 mm

The above described ordered sheet metal packings of type B1-125.80 andB1-250.60 were used.

-   1B₁) An ordered sheet metal packing of type B1-125.80, that is to    say having a specific surface area of 125 m²/m³ and an angle of 80°    to the horizontal was packed with the abovementioned catalyst    particles to fill 80% of the superficial volume. The ordered packing    had a hydraulic diameter of 19 mm. The catalyst was able to be    introduced very readily and in the dry state also trickled out again    completely. The ratio of the equivalent particle diameter of the    catalyst particles to the hydraulic diameter of the ordered packing    was 4.5.-   1B₂) An ordered packing of type B1-250.60, that is to say having a    specific surface area of 250 m²/m³ and an angle of 60° to the    horizontal was packed with the abovementioned catalyst particles to    fill 50% of its superficial volume. The ordered packing had a    hydraulic diameter of 9.4 mm. The catalyst was able to be introduced    very readily and in the dry state also trickled out again    completely. The ratio of the equivalent diameter of the catalyst    particles to the hydraulic diameter of the ordered packing was 2.4.

In contrast, in the case of commercially conventional catalyst packingsin which the catalyst is introduced in pockets, for example of the typeKatapak from Sulzer or Multipack from Montz, only from 20 to 30% of thesuperficial volume, in exceptional cases, a maximum of 50% of thesuperficial volume, could be packed with catalyst.

Example 2 Pressure Drop Measurements

In a column section of diameter 0.1 m, pressure drop measurements weremade using the test mixture nitrogen/isopropanol. For this, the catalystbed was introduced into the column section and irrigated (one dripposition) with a defined amount of isopropanol. In countercurrent tothis, a defined amount of nitrogen was passed through the orderedpacking/bed from bottom to top. In the experiments the specific pressuredrop per unit height of ordered packing or bed was measured and theflooding point was determined. The catalyst particles used were solidγ-Al₂O₃ cylinders. The solid cylinders (d=1.5 mm, h=1-4 mm) had anequivalent particle diameter of 2 mm. The specific pressure drop and theflooding point of a bed introduced into a structured packing were thendetermined.

Example 2 Comparative Example

B01/0732PCBR

At a bed height of 45 cm, at an F factor of 0.038 Pa^(10.5)(corresponding to a gas flow rate of 1 000 l/h) and a liquid loading of0.178 m³/m²h (corresponding to a liquid flow rate of 1.4 l/h), aspecific pressure drop of 3.33 mbar/m was measured. The ordered packingbegan to flood, at a constant liquid loading of 0.178 m³/m²h from an Ffactor of 0.0575 Pa^(10.5) (corresponding to a gas flow rate of 1 500l/h).

Example 2 According to the Invention

Bed introduced into two layers, offset by 90°, of a structured packingof type BS-250.60 from Montz.

At a bed height of 46 cm, at an F factor of 0.038 Pa^(10.5)(corresponding to a gas flow rate of 1 000 l/h) and a liquid loading of0.178 m³/m²h (corresponding to a liquid flow rate of 1.4 l/h), aspecific pressure drop of 1.09 mbar/m was measured. The ordered packingbegan to flood, at a constant liquid loading of 0.178 m³/m²h from an Ffactor of 0.114 Pa^(10.5) (corresponding to a gas flow rate of 3 000l/h). The maximum gas loading could thus be increased by a factor of 2compared with the bed which was not introduced into an ordered packing.

Below, with reference to FIG. 2, the calculation of the hydraulicdiameter for an ordered packing having linear corrugations is described:

The ordered sheet metal packing 2 shown by way of example in FIG. 2 haslinear corrugations 5 arranged in parallel to one another, whichcorrugations subdivide the ordered sheet metal packing 2 into corrugatedsurfaces 6. The width of a corrugated surface 6, measured fromcorrugated edge 5 to corrugated edge 5, is designated a, the distancebetween two sequential corrugated edges 5 is designated c and the heightof the corrugation is designated h. The hydraulic diameter of the gasflow for an ordered packing made up of such ordered-sheet metal packingsis then calculated using the equation$d_{{hydraulic},{gas}} = \frac{2{c \cdot h}}{c + {2a}}$

Example 3 Preparation of Pseudoionone by Aldolization of Citral andAcetone

The experimental set up corresponded to the diagrammatic representationin FIG. 4. The reactive distillation column 7 was packed in each of theseparation zones 8 with one segment of a structured fabric packing oftype A3-500 from Montz, having a total height in each case of 23 cm. Thereaction zone 9 was fitted in the lower region of the same with onelayer of Montz-Pak type B1-1000 in a special element height of 30 mm.This layer served as catalyst barrier so that the catalyst particlescould not trickle into the lower separation zone. On this layer wereinstalled three layers of Montz-Pak from type B1-250.60 having anelement height of 212 mm, into which the catalyst was introduced byloose packing. 3121 g of catalyst were packed in this case at a bulkdensity of 700 kg/m³. The catalyst used was solid cylinders of 5%praseodymium on γ-Al₂O₃ having a particle diameter of 1.5 mm and aheight of from 1 to 4 mm, which had been prepared by impregnatingγ-Al₂O₃ with an aqueous solution of praseodymium nitrate and subsequentcalcination. The column was fitted at regular intervals withthermocouples and with sampling points, so that the temperature profileand concentration profile in the column could be determined.

The reactants citral and acetone (streams I and II, respectively, inFIG. 4) were metered into the reactive distillation column fromreservoir vessels standing on balances, with mass flow controlled by apump.

The bottoms reboiler 10 which was heated to 124° C. using a thermostathad a holdup from 50 to 150 ml during operation, depending on residencetime. The bottoms stream III was transported under level control by apump from the bottoms reboiler 10 into a vessel standing on a balance.

The overhead stream from the reactive distillation column was condensedin a condenser 11 which was operated using a cryostat. A portion of thecondensate passed via a reflux divider, as stream IV, into a reservoirvessel standing on a balance, while the other portion was applied to thecolumn as reflux. The apparatus was equipped with a pressure controllerPC and designed for a system pressure of 20 bar. All influent andeffluent streams were continuously detected and recorded during theentire experiment using a process control system PCS. The apparatus wasoperated continuously in 24 hour operations.

A stream I of 220.0 g/h, equivalent to 1.4 mol/h of citral having apurity of 97%, and a stream II of 840.0 g/h, equivalent to 14.32 mol/hof acetone preheated to 80° C. of a purity of 99% were continuouslyapplied to the above described reactive distillative column 7.

Experimental Procedure

The catalyst used in the reaction zone 9 was solid cylinders (d=1.5 mm,h=1-4 mm) of 5% Pr on γ-Al₂O₃. A system pressure of 3 bar and a refluxratio of 3 kg/kg was set. The bottom temperature was 92.5°. The bottomstream III of the column obtained was 735.6 g/h of crude productcontaining 62.14% by weight of acetone, 0.71% by weight of water, 0.45%by weight of mesityl oxide, 0.95% by weight of diacetone alcohol, 9.14%of citral, 24.43% of pseudoionone and 2.18% by weight of high boilers.At the top of the column, 323.2 g/h of distillate (stream IV) were takenoff, consisting of 95.8% by weight of acetone and 4.2% by weight ofwater.

Pseudoionone was obtained with a selectivity of 97.3% based on citraland 84.4% based on acetone. The yield was 66.7% based on citral.

At F factors of 0.12 Pa^(10.5) and liquid loadings of 0.3 m³/m²h, adifferential pressure of approximately 1 mbar was measured over thecolumn.

When an uncontrolled catalyst bed without ordered packing was used, incomparison twice the pressure drop was measured.

The differential pressure is a measure of the loading (gas and liquid)of the column. Depending on material properties and the type ofinternals used, the differential pressure increases with increasingloading until flooding occurs. In the flooding state, the catalyst isswirled up and high catalyst abrasion can occur. This state musttherefore be avoided.

When the inventive ordered packing is used, therefore, a higherthroughput can be achieved for the same column diameter.

1-10. (Cancelled)
 11. A column for carrying out reactive distillationsin the presence of a heterogeneous particulate catalyst having anordered packing formed from ordered sheet metal packings which formintermediate spaces in the column interior, wherein the column has firstand second part regions which are arranged in alternation and whichdiffer by the specific surface area of the ordered sheet metal packingsin such a manner that in the first part regions the quotient ofhydraulic diameter for the gas stream through the ordered packing andequivalent diameter of the catalyst particles is in the range from 2 to20, preferably in the range from 5 to 10, with the catalyst particlesbeing introduced into the intermediate spaces, distributed anddischarged loose under the action of gravity and in the second partregions the quotient of the hydraulic diameter for the gas streamthrough the ordered packing and equivalent diameter of the catalystparticles is less than 1 and no catalyst particles are introduced intothe second part regions.
 12. A column as claimed in claim 11, whereinthe ordered packing is a structured packing.
 13. A column as claimed inclaim 12, wherein the structured packing is a cross-channel packing. 14.A column as claimed in claim 11, wherein the ordered packing hashorizontal surface portions.
 15. A column as claimed in claim 14, theordered packing is formed from ordered sheet metal packings for verticalinstallation into the column having linear corrugations which subdividethe ordered sheet metal packing into corrugated surfaces, wherein theangle of inclination of the corrugated surfaces to the horizontal is inthe range from 90° to 45°.
 16. A column as claimed in claim 11, whereinthe ordered packing has a reduced resistance to flow at its surface. 17.A column as claimed in claim 12, wherein the ordered packing is formedfrom rippled or corrugated layers, and between two rippled or corrugatedlayers in each case one flat intermediate layer is disposed, with theflat intermediate layers not extending to the edge of the orderedpacking or having, in the edge zone of the ordered packing, an increasedgas permeability.
 18. A column as claimed in claim 12, wherein theordered packing is formed from ordered sheet metal packings for verticalinstallation into the column having linear corrugations which subdividethe ordered sheet metal packings into corrugated surfaces and which havea width a, measured from corrugated edge to corrugated edge andperforations, wherein a proportion X of at least 60% of the perforationshas a distance b of at most 0.4 a to the lower corrugated edge of eachcorrugated surface.
 19. A process for reactive distillation in a columnas claimed in claim 11, which comprises operating the column withrespect to its gas and liquid loadings in such a manner that a maximumof from 50 to 95% of the flooding limit loading is reached.
 20. Aprocess as claimed in claim 19, wherein the reactive distillation is aheterogeneously catalyzed reactive distillation.
 21. A column as claimedin claim 11, wherein in the first part regions the quotient of hydraulicdiameter for the gas stream through the ordered packing and equivalentdiameter of the catalyst particles is in the range from 5 to
 10. 22. Acolumn as claimed in claim 15, wherein the angle of inclination of thecorrugated surfaces to the horizontal is 60°.
 23. A column as claimed inclaim 16, wherein the reduced resistance to flow at the surface of theordered packing is due to perforations and/or roughness of the materialof the ordered packing or by constructing the ordered packing asexpanded metal.
 24. A column as claimed in claim 17, wherein theincreased gas permeability in the edge zone of the ordered packing isdue to holes.
 25. A process as claimed in claim 20, wherein theheterogeneously catalyzed reactive distillations are acid- orbase-catalyzed equilibrium reactions.
 26. A process as claimed in claim25, wherein the heterogeneously catalyzed reactive distillation is thepreparation of pseudoionone by aldolizing citral and acetone in thepresence of an aluminum-oxide-supported praseodymium catalyst.